Genetic mutations in presenilins (PSs, PS1/PS2) account for the majority of early-onset familial Alzheimer's disease (FAD). PS is the putative catalytic component of gamma-secretase complex. Gamma-secretase mediates the intramembrane cleavage of amyloid precursor protein (APP) that generates pathogenic small peptide Abeta in Alzheimer's disease (AD). So far, PSs, Nicastrin (Net), Aph-1, and PEN-2 have been identified as its essential components. They are integral membrane proteins that are synthesized in ER and travel through the secretory pathway. PS1 has been shown to play roles in intracellular trafficking of gamma-secretase component Net. In my preliminary studies, I found that in the absence of PS, PEN-2 is retained in the ER with a shorter half-life, suggesting PS is required for the trafficking and stability of PEN-2, probably via physical interaction. Furthermore, certain gamma-secretase inhibitor treatment results in markedly increased cell surface bound PS1 and PEN-2, but not Net. This is the first time that highly selective potent gamma-secretase inhibitors has been shown to differentially affect the trafficking of gamma-secretase components. Since these gamma-secretase inhibitors have been shown to physically bind PS1,I hypothesized that their effect on the gamma-secretase components is mediated by PS1. Indeed, my preliminary data further demonstrated that the inhibitor-induced cell surface accumulation of PEN-2 depends on PS1. Based on these results, I propose that PS and its associated gamma-secretase activity are critical for maintaining the integrity and proper intracellular trafficking of the gamma-secretase complex. The objective of this proposal is therefore to test this hypothesis. The impact of altered PS1 function by PS1 mutation (Specific Aim1) on the integrity and trafficking property of gamma-secretase complex will be systemically examined. These studies will reveal the mechanism of the cellular perturbation underlying PS1 mutations, including which results in pathogenesis of AD. Furthermore, detailed analysis of how gamma-secretase inhibitors affect the trafficking of gamma-secretase components (Specific Aim 2), especially whether they have the same effect toward PS1 mutants (Specific Aim 3) should provide valuable information for drug design to slow and ultimately prevent AD.